1. Field of the Invention
The present invention relates to a thin-film magnetic head and, more particularly, to thin-film magnetic heads which can simultaneously trace two tracks.
2. Description of the Prior Art
Recently, as an apparatus for recording and reproducing a still picture, a magnetic recording and reproducing apparatus using a magnetic disk has been proposed.
In such an apparatus, a still video signal of one field is generally recorded in one circular track which circles the magnetic disk. However, in the case where the diameter of magnetic disk is small as the apparatus becomes small-sized or the like, such a signal cannot be recorded in one circular track to ensure a sufficient recording density, so that it is necessary to record the still video signal of one field in two tracks.
In this case, it is obviously desirable to use magnetic heads which can simultaneously record and reproduce the signal.
On the other hand, in case of recording a still video signal of two fields, i.e., one frame, even in the case where the video signal of one field is recorded in one circular track and the still picture is recorded and reproduced by use of two circular tracks, it is desirable that the magnetic heads can simultaneously trace two tracks.
However, when such magnetic heads which can simultaneously trace two tracks are constructed as conventional bulk types having, ring-like magnetic cores, there is a large amount of crosstalk between two tracks since a pair of bulk type magnetic cores are extremely closely arranged, so that this causes a practical problem.
Therefore, use is made of thin-film magnetic heads which can be constituted as extremely small-sized heads as compared with the bulk type magnetic heads.
Thin-film magnetic heads have many advantages such that: they can be formed by various kinds of thin-film depositing methods similar to the semiconductor manufacturing process; working accuracy is remarkably good; a plurality of heads can be extremely easily formed on the same substrate; mass production is possible; and uniform products can be derived.
Therefore, thin-film magnetic heads are widely used in information equipment including an external storage device of an electronic computer, video tape recorders, magnetic recording camera, etc. as the magnetic recording is performed at a high density.
FIG. 1 shows a conventional structure of conventional thin-film magnetic heads.
FIG. 1 illustrates an example of heads which can simultaneously trace two tracks and the conductors of which are spirally formed such that they are turned three times.
In FIG. 1, a numeral 1 denotes a magnetic substrate and conductors 6 are formed on the magnetic substrate 1 such that they are turned three times. Recording currents are supplied to the conductors 6 from electrodes 7 also formed on the magnetic substrate 1.
On the other hand, a numeral 4 represents upper magnetic layers which consist of magnetic thin films and form the other magnetic yokes as parts of magnetic circuits of the magnetic heads. Respective ends of the upper magnetic layers 4 are fixed to the sides of contact holes 2 formed at central portions of the spiral conductors 6, thereby providing the magnetic junctions with the magnetic substrate 1. The other ends are fixed in the manner such that they face the side of edge portions of the magnetic substrate 1, thereby forming magnetic gaps 5 between the edge portions of the upper magnetic layers 4 and the edge portions of the magnetic substrate 1.
The respective layers which are formed on and over the magnetic substrate 1 shown in FIG. 1 are formed by the thin-film depositing method and photolithography, respectively.
In FIG. 1, the insulation layers between the respective layers are omitted.
For magnetic recording by use of such thin-film magnetic heads, magnetic fields are generated on the sides of magnetic gaps 5 by allowing recording current to flow through the conductors 6 from the electrodes 7, thereby magnetizing a magnetic recording medium (not shown) which is located near the gap portions. Thus, the magnetic recording is performed.
On the other hand, for reproducing the signals magnetically recorded, the magnetic fluxes generated form the recorded and magnetized portions on the magnetic recording medium which are located near the magnetic gaps 5 pass through the magnetic substrate 1 and upper magnetic layers 4 and cross the conductors 6. These magnetic fluxes are changed as the magnetic recording medium is moved, causing voltages to be induced between the conductors 6 and the electrodes 7. Therefore, reproduction is performed by detecting these voltages.
The crosstalk between the tracks occurs due to two reasons: the coils of the two tracks have direct magnetic coupling; and the magnetic flux leaps between the magnetic yokes of the two tracks.
The crosstalk due to the leap of the magnetic flux between the magnetic yoke increases as the facing areas of magnetic yokes increase.
On the other hand, in the thin-film magnetic heads, thicknesses of magnetic yokes are small and those facing areas can be made remarkably smaller than those of bulk heads; therefore, a decrease in crosstalk can be expected.
However, when the thicknesses of upper magnetic layers 4 as the magnetic yokes and of the magnetic substrate 1 are reduced, the magnetic resistances of the magnetic yoke portions are enlarged, causing a drawback such as deterioration in efficiencies upon recording and reproduction.
To overcome such a drawback, for example, it is necessary to set the widths in the directions of tracks of upper magnetic layers 4 to be large. However, when such a structure is adopted, the portion where the magnetic yokes of both tracks approach becomes long, so that crosstalk easily occurs and cannot be reduced below, e.g., -40 dB.
Namely, since the extraction electrodes extracted from the two heads are alternately formed on the substrate in the same repetitive pattern, the extraction electrodes of the two heads are not symmetric with respect to the right and left sides and the mutual distributed capacitances are not equal. Thus, there is the drawback that the electromagnetic conversion characteristics of the two heads are not balanced.